Often in using digital logic circuitry there is a need to reset a circuit, such as a digital counter, that has been burned off. If the digital counter is turned off but then turned on quickly thereafter, it may happen that the reset circuitry has not functioned and that when the circuit is turned on it has not been completely reset. For example, assume that the digital counter has counted to 100. The counter is then turned off but turned back on promptly thereafter. Although it is desired that the counter now be at zero, because of the rapid turn-on the reset circuitry may not have recovered and the counter may be at an arbitrary number rather than zero. This problem is particularly found when a reset circuit is used requiring a capacitor discharge. In such circuits, if the power supply is turned off, the supply voltage will decrease rapidly to zero. However, such capacitor circuits utilize a capacitor which must be discharged to below a certain point before the circuit can properly be reset again.
In sterilization apparatus, it is particularly important that time or quantity measurements be made accurately and that the digital logic circuitry, such as the digital counters, which may be utilized in making such measurements, be reset properly. For example, if a counter measuring the amount of ultraviolet radiation which has been used to sterilize an item has not been reset properly, the sterilization may be incomplete because the counter may not have started counting at its zero point.
It is, therefore, an object of the present invention to provide a circuit which resets a digital logic circuit, without being dependent on a storage element such as a capacitor to generate the reset signal.
Another object of the present invention is to provide a rapid reset for digital logic circuitry and a self-test to determine whether this rapid reset has actually occurred.
Other objects and advantages of the invention will become apparent as the description proceeds.